It sounds like the file should be in the joomla root. My guess is that your config pointed to 127.0.0.1 and that's no longer where your DB is. There's also the case of some DBs defaulting to only allowing access from specific hosts.

Normally localhost is included, but If you do have the right IP for the DB in your config, then I bet the SQL server isn't allowing connections from the new website's IP.